Osteoporosis is a disease characterized by increased bone fragility and deteriorating bone micro-architecture. The main consequence of osteoporosis is low-trauma fractures, most often of the hip, spine and wrist. Recently, another type of low-trauma fracture, atypical femur fractures (AFFs), have received much attention. Little is known of the cause of these debilitating fractures; however, they have been associated with long term bisphosphonate use. What we currently know about AFFs is based on case reports or small case series, or studies using administrative databases or secondary analyses of bisphosphonate trials. While these reports provide some preliminary information on the relationship between long term bisphosphonate exposure and AFFs, detailed clinical data are absent. As we have established a network of specialists across southern Ontario our group is in a position to collect meaningful information on a larger group of patients who have experienced these debilitating fractures into a centralized AFF registry.